title: Synthesis and structural determination of zinc complexes based on an anilido-aldimine ligand containing an O-donor pendant arm: zinc alkoxide derivative as an efficient initiator for ring-opening polymerization of cyclic esters.
abstract: Zinc complexes bearing the anilido-aldiminate AA(OMe) ligand (AA(OMe)-H = (E)-2,6-diisopropyl-N-(2-(((2-methoxyethyl)imino)methyl)phenyl)aniline) were synthesized in a stepwise method and were structurally characterized. The reaction of AA(OMe)-H (1) with one equivalent of diethyl zinc (ZnEt2) furnishes a three-coordinated and mononuclear zinc complex [(AA(OMe))ZnEt] (2). Further reaction of 2 with a stoichiometric amount of benzyl alcohol (BnOH) affords a four-coordinated and dinuclear zinc benzylalkoxide complex [(AA(OMe))Zn(μ-OBn)]2 (3). In the presence of two equivalents of AA(OMe)-H with ZnEt2, a homoleptic and four-coordinated zinc complex [(AA(OMe))2Zn] (4) is formed. The geometry around the zinc centres of 3 and 4 are both distorted tetrahedrals, while 2 adopts a different coordination mode with a slightly distorted trigonal planar geometry. The variable-temperature (1)H NMR studies of 3 illustrate that 3 exhibits a dinuclear structure in solution at low temperature as well as in the solid state. While raising the temperature, it drifts towards dissociation to form a mononuclear zinc benzylalkoxide species, which coexists in solution. The ring-opening polymerizations of ε-caprolactone (ε-CL) and β-butyrolactone (β-BL) catalyzed by complexes 3 and 4 are investigated. The ε-CL and β-BL polymerizations initiated by zinc alkoxide 3 were demonstrated to have living characteristics and to proceed in a controlled manner with narrow polydispersity indices (PDIs < 1.12). An efficient catalytic performance for the β-BL polymerization with a high monomer-to-initiator ratio (1200/1) initiated by 3 has also been reported.
authors.affiliation: Department of Chemistry, Chung Yuan Christian University, Chung-Li 320, Taiwan.
authors.forename: Chao-Hsiang
authors.initials: CH
authors.lastname: Wang
authors.forename: Chen-Yu
authors.initials: CY
authors.lastname: Li
authors.forename: Bor-Hunn
authors.initials: BH
authors.lastname: Huang
authors.forename: Chu-Chieh
authors.initials: CC
authors.lastname: Lin
authors.forename: Bao-Tsan
authors.initials: BT
authors.lastname: Ko
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D003500:Cyclization; D004355:Drug Stability; D004952:Esters / Q000737:chemistry*; D008024:Ligands; D010100:Oxygen / Q000737:chemistry; D058105:Polymerization; D015032:Zinc / Q000737:chemistry*
chemical_list: D000814:Aniline Compounds; D056831:Coordination Complexes; D004952:Esters; D008024:Ligands; D015032:Zinc; D010100:Oxygen; C023650:aniline